This invention relates to apparatus for measuring the contact normal force imposed by a receptacle contact on a pin received therein and in particular to a normal force transducer including a monocrystalline silicon beam.
U.S. Pat. No. 4,380,171 discloses apparatus for measuring the contact normal force between a resilient contact in a card edge connector and a pad on a printed circuit board received therein. A blade-like probe is substantially the same thickness as the printed circuit board. The probe has a base and a distal end and comprises two members defining an open space therebetween. One of the members has parallel slots defining a fixed end beam adjacent the space. The beam has a pair of strain gauges bonded thereto toward opposed ends, the gauges being connected by leads which further extend into the base for connection to current supply means and galvanometer means remote from the probe. The circuit forms a balanced bridge when the beam is not loaded. An unbalanced bridge results when the probe is inserted in a card edge connector where the beam is loaded by the normal force applied thereto by the resilient contact of the connector. The contact normal force may thus be determined by well known principles as outlined in Perry, C. C., The Strain Gauge Primer (McGraw-Hill, 1962) at pages 55-73.
U.S. Pat. No. 4,667,512 enables measuring the normal force provided by contacts which receive 0.025 inch square posts. The normal force transducer disclosed in U.S. Pat. No. 4,667,512 is not adaptable for receptacle contacts which receive a substantially smaller post, such as a 0.0156 inch thick post. Contacts of this thickness are prevalent such as in connectors manufactured and sold by the assignee in its AMPLIMITE 0.050 Series connector line. It would accordingly be desirable to have a measuring device with a probe profiled as a pin means for measuring the normal force imposed by receptacle contacts on a 0.0156 inch thick post. As beams are made smaller and smaller, the beams are of reduced stiffness. Therefore, additional stiffness must be provided from the sensing element.